> On Aug 17, 2021, at 3:43 AM, Richard Biener <[email protected]> wrote:
>
> On Mon, 16 Aug 2021, Qing Zhao wrote:
>
>>
>>
>>> On Aug 16, 2021, at 2:40 AM, Richard Biener <[email protected]> wrote:
>>>
>>> On Thu, 12 Aug 2021, Qing Zhao wrote:
>>>
>>>> Hi, Richard,
>>>>
>>>> For RTL expansion of call to .DEFERRED_INIT, I changed my code per your
>>>> suggestions like following:
>>>>
>>>> ======================
>>>> #define INIT_PATTERN_VALUE 0xFE
>>>> static void
>>>> expand_DEFERRED_INIT (internal_fn, gcall *stmt)
>>>> {
>>>> tree lhs = gimple_call_lhs (stmt);
>>>> tree var_size = gimple_call_arg (stmt, 0);
>>>> enum auto_init_type init_type
>>>> = (enum auto_init_type) TREE_INT_CST_LOW (gimple_call_arg (stmt, 1));
>>>> bool is_vla = (bool) TREE_INT_CST_LOW (gimple_call_arg (stmt, 2));
>>>>
>>>> tree var_type = TREE_TYPE (lhs);
>>>> gcc_assert (init_type > AUTO_INIT_UNINITIALIZED);
>>>>
>>>> if (is_vla || (!can_native_interpret_type_p (var_type)))
>>>> {
>>>> /* If this is a VLA or the type of the variable cannot be natively
>>>> interpreted, expand to a memset to initialize it. */
>>>> if (TREE_CODE (lhs) == SSA_NAME)
>>>> lhs = SSA_NAME_VAR (lhs);
>>>> tree var_addr = NULL_TREE;
>>>> if (is_vla)
>>>> var_addr = TREE_OPERAND (lhs, 0);
>>>> else
>>>> {
>>>> TREE_ADDRESSABLE (lhs) = 1;
>>>> var_addr = build_fold_addr_expr (lhs);
>>>> }
>>>> tree value = (init_type == AUTO_INIT_PATTERN) ?
>>>> build_int_cst (unsigned_char_type_node,
>>>> INIT_PATTERN_VALUE) :
>>>> build_zero_cst (unsigned_char_type_node);
>>>> tree m_call = build_call_expr (builtin_decl_implicit (BUILT_IN_MEMSET),
>>>> 3, var_addr, value, var_size);
>>>> /* Expand this memset call. */
>>>> expand_builtin_memset (m_call, NULL_RTX, TYPE_MODE (var_type));
>>>> }
>>>> else
>>>> {
>>>> /* If this is not a VLA and the type of the variable can be natively
>>>> interpreted, expand to assignment to generate better code. */
>>>> tree pattern = NULL_TREE;
>>>> unsigned HOST_WIDE_INT total_bytes
>>>> = tree_to_uhwi (TYPE_SIZE_UNIT (var_type));
>>>>
>>>> if (init_type == AUTO_INIT_PATTERN)
>>>> {
>>>> unsigned char *buf = (unsigned char *) xmalloc (total_bytes);
>>>> memset (buf, INIT_PATTERN_VALUE, total_bytes);
>>>> pattern = native_interpret_expr (var_type, buf, total_bytes);
>>>> gcc_assert (pattern);
>>>> }
>>>>
>>>> tree init = (init_type == AUTO_INIT_PATTERN) ?
>>>> pattern :
>>>> build_zero_cst (var_type);
>>>> expand_assignment (lhs, init, false);
>>>> }
>>>> }
>>>> ===========================
>>>>
>>>> Now, I used “can_native_interpret_type_p (var_type)” instead of
>>>> “use_register_for_decl (lhs)” to decide
>>>> whether to use “memset” or use “assign” to expand this function.
>>>>
>>>> However, this exposed an bug that is very hard to be addressed:
>>>>
>>>> *******For the testing case: test suite/gcc.dg/uninit-I.c:
>>>>
>>>> /* { dg-do compile } */
>>>> /* { dg-options "-O2 -Wuninitialized" } */
>>>>
>>>> int sys_msgctl (void)
>>>> {
>>>> struct { int mode; } setbuf;
>>>> return setbuf.mode; /* { dg-warning "'setbuf\.mode' is used" } */
>>>> ==
>>>>
>>>> ******the above auto var “setbuf” has “struct” type, which
>>>> “can_native_interpret_type_p(var_type)” is false, therefore,
>>>> Expanding this .DEFERRED_INIT call went down the “memset” expansion route.
>>>>
>>>> However, this structure type can be fitted into a register, therefore
>>>> cannot be taken address anymore at this stage, even though I tried:
>>>>
>>>> TREE_ADDRESSABLE (lhs) = 1;
>>>> var_addr = build_fold_addr_expr (lhs);
>>>>
>>>> To create an address variable for it, the expansion still failed at
>>>> expr.c: line 8412:
>>>> during RTL pass: expand
>>>> /home/opc/Work/GCC/latest-gcc/gcc/testsuite/gcc.dg/auto-init-uninit-I.c:6:24:
>>>> internal compiler error: in expand_expr_addr_expr_1, at expr.c:8412
>>>> 0xd04104 expand_expr_addr_expr_1
>>>> ../../latest-gcc/gcc/expr.c:8412
>>>> 0xd04a95 expand_expr_addr_expr
>>>> ../../latest-gcc/gcc/expr.c:8525
>>>> 0xd13592 expand_expr_real_1(tree_node*, rtx_def*, machine_mode,
>>>> expand_modifier, rtx_def**, bool)
>>>> ../../latest-gcc/gcc/expr.c:11741
>>>> 0xd05142 expand_expr_real(tree_node*, rtx_def*, machine_mode,
>>>> expand_modifier, rtx_def**, bool)
>>>> ../../latest-gcc/gcc/expr.c:8713
>>>> 0xaed1d3 expand_expr
>>>> ../../latest-gcc/gcc/expr.h:301
>>>> 0xaf0d89 get_memory_rtx
>>>> ../../latest-gcc/gcc/builtins.c:1370
>>>> 0xafb4fb expand_builtin_memset_args
>>>> ../../latest-gcc/gcc/builtins.c:4102
>>>> 0xafacde expand_builtin_memset(tree_node*, rtx_def*, machine_mode)
>>>> ../../latest-gcc/gcc/builtins.c:3886
>>>> 0xe97fb3 expand_DEFERRED_INIT
>>>>
>>>> ******That’s the major reason why I chose “use_register_for_decl(lhs)” to
>>>> decide “memset” expansion or “assign” expansion, “memset” expansion
>>>> needs to take address of the variable, if the variable has been decided to
>>>> fit into a register, then its address cannot taken anymore at this stage.
>>>>
>>>> ******using “can_native_interpret_type_p” did make the “pattern”
>>>> generation part much cleaner and simpler, however, looks like it didn’t
>>>> work correctly.
>>>>
>>>> Based on this, I’d like to keep my previous implementation by using
>>>> “use_register_for_decl” to decide whether to take “memset” expansion or
>>>> “assign” expansion.
>>>> Therefore, I might still need to keep the “UGLY” implementation of
>>>> generatting “pattern” constant for different types?
>>>>
>>>> Let me know your opinion on this.
>>>
>>> Hmm, I think you can use use_register_for_decl(lhs) to decide to use an
>>> alternate type to generate the pattern (and feed to
>>> can_native_interpret_type_p) by using
>>> lang_hooks.type_for_mode (TYPE_MODE (TREE_TYPE (lhs))).
>>
>> Do you mean that the TYPE returned by “lang_hooks.type_for_mode(TYPE_MODE
>> (TREE_TYPE (lhs))” will always satisfy “can_native_interpret_type_p”?
>> Even for big structure types?
>
> I meant that for use_register_for_decl (lhs) the structures will be
> always small and the structure type will have a mode that is not BLKmode
> (but for example DImode for struct { int i; int j; }).
Oh, I see.
>
>> i.e,
>>
>> tree var_type = TREE_TYPE(lhs);
>> tree pattern = NULL_TREE;
>> unsigned HOST_WIDE_INT total_bytes
>> = tree_to_uhwi (TYPE_SIZE_UNIT (var_type));
>>
>> If (use_register_for_decl(lhs)==false)
>> {
>> tree alt_type = lang_hooks.type_for_mode(TYPE_MODE(var_type),
>> TYPE_UNSIGNED(var_type);
>> If (can_native_interpret_type_p (alt_type))
>> {
>> unsigned char *buf = (unsigned char *) xmalloc (total_bytes);
>> memset (buf, INIT_PATTERN_VALUE, total_bytes);
>> pattern = native_interpret_expr (alt_type, buf, total_bytes);
>> gcc_assert (pattern);
>> }
>> else
>> gcc_unreachable ();
>> }
>>
>> ?
>> Don’t quite understand here. Please clarify.
>
> For !use_register_for_decl you use memset already, but for
> use_register_for_decl not all types satisfy can_native_interpret_type_p
> (in particular all struct and union types). But when we use a
> register for the decl then we can of course directly initialize the
> register.
So, you mean the following:
If (is_vla || (!use_register_for_decl (lhs)))
{
/* expand as memset that is done currently. */
}
else
{
tree alt_type = lang_hooks.type_for_mode(TYPE_MODE(var_type),
TYPE_UNSIGNED(var_type);
If (can_native_interpret_type_p (alt_type))
{
unsigned char *buf = (unsigned char *) xmalloc (total_bytes);
memset (buf, INIT_PATTERN_VALUE, total_bytes);
pattern = native_interpret_expr (alt_type, buf, total_bytes);
gcc_assert (pattern);
}
else
gcc_unreachable ();
tree init = (init_type == AUTO_INIT_PATTERN) ?
pattern :
build_zero_cst (alt_type);
/* here build VIEW_CONVERT <alt_type> (lhs) = init;
And then expand it. */
}
?
> As said, it would be much cleaner (and maybe also easier)
> to then simply expand the RTL directly rather than going through
> expand_assignment.
Dump questions here:
1. When building VIEW_CONVERT <alt_type> (lhs) = init and expand it:
Is the following correct:
lhs = build1 (VIEW_CONVERT_EXPR, alt_type, lhs);
expand_assignment (lhs, init);
which utility routines should be used to building the assignment and then
expand it?
Are the above utility routines correct?
> It's also easier to directly see whether the
> LHS is a MEM_P or a REG_P but then for the MEM_P case it's a bit
> more "awkward" to use the easy way of the generic expand code
> (esp. if we eventually want to emit actual calls to memset - do we?)
If all these are guarded by “use_register_for_decl” already, the lhs should be
fit into registers,
Under such situation, I don’t think that we want to emit actual calls to
memset. That’s too expensive.
>
>>> You can then
>>> build the assignment from the pattern as
>>>
>>> VIEW_CONVERT <reg-type> (lhs) = pattern_cst;
>>
>> What’s the <reg_type> in the above? The type “alt_type” returned by
>> “lang_hooks.type_for_mode(TREE_TYPE(lhs))?
>> Do I need to build “MODIFY_EXPR” for the above?
>
> Yes, the lang_hook.type_for_mode result and no, you could go through
> expand_assignment.
Okay. So, still use “expand_assigment” to expand it?
>
>> lhs = build1 (VIEW_CONVERT_EXPR, alt_type, lhs);
>> tree final = build2 (MODIFY_EXPR, TREE_TYPE (alt_type), lhs, pattern);
>>
>> Then how to expand this”final"?
>>>
>>> note that more RTL-expand-ish would be to simply expand 'lhs' and
>>> see whether it's a REG_P or a MEM_P and decide based on that.
>>
>> You mean that the current RTL expansion will automatically expand LHS to
>> memset route or assignment route based on whether
>> LHS is a REG_P or MEM_P? I don’t need to explicitly code for
>> “expand_builtin_memset” or “expand_assign”?
>
> No. But you are inside the expander for the internal function call
> and this is expected to generate RTL. You can simply generate
> RTL directly without "faking" new GENERIC calls or assignments and
> expanding those.
>
> But lets not go there for now.
Okay. I see now.
Qing
>
> Richard.
